If you go usually to karaokes or sing in the shower you must try midomi.com. This website recognizes the song you’re singing or humming, and reviews say it usually get it correctly.
Behind this, midomi.com tries to build a community of people with the same musical style taste and a database of searchable songs. You can upload your song online, you only need to have a mic (and soundcard, of course) or upload a recorded file.
I don’t really know if people will build a community behind this, I thought people would build a community behind services like Pandora or last.fm.